The word deuterocanonical comes from the Greek meaning 'belonging to the second canon'. The etymology of the word is misleading, but it does indicate the hesitation with which these books were accepted into the canon by some.

Strictly, the term does not mean non-canonical; accordingly, many who do not accept these books as part of the canon of Scripture designate them instead by the term "Apocrypha", and either omit them from the Bible or include them in a section designated Apocrypha. This difference in terminology sometimes causes confusion.

Catholicism

Deuterocanonical is a term first coined in 1566 by the theologian Sixtus of Siena, who had converted to Catholicism from Judaism, to describe scriptural texts of the Old Testament whose canonicity was explicitly defined for Catholics by the Council of Trent, but which had been omitted by some early canon lists, especially in the East. Their acceptance among early Christians was not universal, but regional councils in the West published official canons that included these books as early as the fourth and fifth centuries. The canon of Trent confirmed these early western canons.

The Catholic deuterocanonical scriptural texts as defined by the Council of Trent are:

Differences from Apocrypha

There is a great deal of overlap between the Apocrypha section of the 1611 King James Bible and the Catholic deuterocanon, but the two are distinct. The Apocrypha section of the King James Bible includes, in addition to the deuterocanonical books, the following three books, which were not declared canonical by Trent:

These three books alone make up the Apocrypha section of the Clementine Vulgate, where they are specifically described as "outside of the series of the canon". The 1609 Douai Bible includes them in an appendix, but they have been dropped from recent Catholic translations into English. They are found, along with the deuterocanonical books, in the Apocrypha section of Protestant bibles.

Using the word apocrypha (Greek: hidden away) to describe texts, although not necessarily pejorative, implies to some people that the writings in question should not be included in the canon of the Bible. This classification commingles them with certain non-canonical gospels and New Testament Apocrypha. The Style Manual for the Society of Biblical Literature recommends the use of the term deuterocanonical literature instead of Apocrypha in academic writing.

Influence of the Septuagint

The large majority of Old Testament references in the New Testament are taken from the Greek Septuagint—which includes the deuterocanonical books, as well as apocrypha—both of which are called collectively anagignoskomena (things that are read) . Several appear to have been written originally in Hebrew, but the original text has long been lost. Archaeological finds in the last century, however, have provided a text of almost two-thirds of the book of Sirach, and fragments of other books have been found as well. The Septuagint was widely accepted and used by Greek-speaking Jews in the first century, even in the region of Roman Judea, and therefore naturally became the text most widely used by early Christians, who were predominantly Greek speaking.

In the New Testament, Hebrews 11:35 refers to an event that was only explicitly recorded in one of the deuterocanonical books (2 Maccabees 7).

Other New Testament authors also quote period literature which was familiar to the audience but that was neither included in the Old Testament or the deuterocanonical books. For instance, Paul cites Greek writers and philosophers, and the author of Hebrews references oral tradition which spoke of Old Testament prophet who was sawn in half in Hebrews 11:37, two verses after the 2nd Maccabees reference.

Some cite 1 Cor 15:29 "Else what shall they do which are baptized for the dead, if the dead rise not at all? why are they then baptized for the dead?", as an allusion to 2 Maccabees 12: 44, "for if he were not expecting the fallen to rise again, it would have been useless and foolish to pray for them in death". 1 Cor 15:29, however, does not reference prayer to help those who are dead be loosed from sin that was committed during life. From verse 11, Paul argues against those who said that there is no resurrection from death. His argument begins with Christ's resurrection in verse 16 "For if the dead are not raised, not even Christ has been raised"; he states in verse 20 that since Christ was resurrected, we also will be "But in fact Christ has been raised from the dead, the firstfruits of those who have fallen asleep." Verse 29 follows in this context, asking why someone would be baptized on behalf of the dead, if the dead are not raised. Using the context of the writing, it may be seen that one would not be baptized into a faith that requires the resurrection of Christ, if that person did not believe that Christ was raised from the dead or that all people would be resurrected. Verse 19 states the meaning plainly "If in Christ we have hope in this life only, we are of all people most to be pitied." (Baptism was the initiation rite of those who had faith in Christ, thus would be absurd if one did not believe in a risen Christ).

However, Josephus (a Jewish historian) speaks of the books as being 22 in number, a Jewish tradition reported also by Athanasius, who, however, included in his list of 22 Old Testament books Baruch and the Letter of Jeremiah. At the same time, he mentioned that certain other books, including five deuterocanonical books but also the Didache and the Shepherd of Hermas, while not being part of the canon, "were appointed by the Fathers to be read". He excluded what he called "apocryphal writings" entirely.

Influence of the Vulgate

Jerome in his prologues describes a canon which excludes the deuterocanonical books, possibly excepting Baruch. However, Jerome's Vulgate did include the deuterocanonical books as well as apocrypha. He referred to them as scriptural and quoted from them despite describing them as "not in the canon". In his prologue to Judith, without using the word canon, he mentioned that Judith was held to be scriptural by the First Council of Nicaea. In his reply to Rufinus, he stoutly defended the deuterocanonical portions of Daniel even though the Jews of his day did not:

What sin have I committed if I followed the judgment of the churches? But he who brings charges against me for relating the objections that the Hebrews are wont to raise against the Story of Susanna, the Song of the Three Children, and the story of Bel and the Dragon, which are not found in the Hebrew volume, proves that he is just a foolish sycophant. For I was not relating my own personal views, but rather the remarks that they [the Jews] are wont to make against us. (Against Rufinus, 11:33 [AD 402]).

Thus Jerome acknowledged the principle by which the canon was settled—the judgment of the Church, rather than his own judgment or the judgment of Jews.

The Vulgate is also important as the touchstone of the canon concerning which parts of books are canonical. When the Council of Trent listed the books included in the canon, it qualified the books as being "entire with all their parts, as they have been used to be read in the Catholic Church, and as they are contained in the old Latin vulgate edition". This decree was clarified somewhat by Pope Pius XI on June 2, 1927, who allowed that the Comma Johanneum was open to dispute, and it was further explicated by Pope Pius XII's Divino Afflante Spiritu.

In the Amharic Bible used by the Ethiopian Orthodox Church (an Oriental Orthodox Church), those books of the Old Testament that are still counted as canonical, but not by all other Churches, are often set in a separate section titled "Deeyutrokanoneekal" (ዲዩትሮካኖኒካል), which is the same word. The Ethiopian Orthodox Deuterocanon, in addition to the standard set listed above, along with the books of Esdras and Prayer of Minasse, also includes some books that are still held canonical by only the Ethiopian Church, including Henok (I Enoch), Kufale (Jubilees) and 1, 2 and 3 Makabis, which are sometimes wrongly confused with the "Books of Maccabees".

Eastern Orthodoxy

The Eastern Orthodox Churches have traditionally included all the books of the Septuagint in their Old Testaments. Regional differences have generally been based on different variations of the Septuagint, as some include more than others.

The Greeks use the word Anagignoskomena to describe those books of the Greek Septuagint which are not present in the Hebrew Tanakh.
These books include the entire Roman Catholic deuterocanon listed above, plus an additional psalm, and the following additional texts:

The Greeks include 4 Maccabees in an appendix, which is not canonical.

Like the Catholic deuterocanonical books, these texts are integrated with the rest of the Old Testament, not printed in a separate section.
Most Protestant Bible versions exclude these books. It is widely believed that Judaism officially excluded the deuterocanonicals and the additional Greek texts listed here from their Scripture in the Council of Jamnia (c.70-90 AD), but this claim is also disputed.

The various Orthodox churches generally include these (originally Greek) texts, and some add the Psalms of Solomon. In the Greek Orthodox Church, 4 Maccabees is relegated to an appendix, because some parts are considered to reflect pagan tendencies.

New Testament

The term deuterocanonical is sometimes used to describe the canonical antilegomena, those books of the New Testament which, like the deuterocanonicals of the Old Testament, were not universally accepted by the early Church, but which are now included in the 27 books of the New Testament recognized by almost all Christians. The deuterocanonicals of the New Testament are as follows: